The solution growth method has been known as a method for producing a single crystal of silicon carbide (SiC). In the solution growth method, an SiC seed crystal, which is to be attached to a lower end surface of a seed shaft, is brought into contact with an SiC solution accommodated in a crucible. Thereafter, the SiC seed crystal is pulled up to grow an SiC single crystal on the SiC seed crystal. The SiC solution as used herein refers to a solution in which carbon (C) is dissolved in a melt of Si or an Si alloy.
In the solution growth method, the temperature in a region of the SiC solution in the vicinity of and directly below an SiC seed crystal which is in contact with the SiC solution (hereafter, simply referred to as a vicinity region) is kept lower than in other regions. Specifically, the lower end portion of the seed shaft is cooled by a coolant (gas or water) flowing through the inside of the seed shaft, or by heat dissipation by the heat conduction through the seed shaft. The lower end portion of the seed shaft thus cooled then cools the SiC seed crystal, and also cools a vicinity region thereof. This causes SiC in the vicinity region to be supersaturated, thereby facilitating the growth of an SiC single crystal. In short, the heat of the vicinity region is dissipated by the seed shaft, thereby placing the vicinity region into a supercooled state.
However, if the temperature in a region other than the vicinity region (hereafter, referred to as a peripheral region) of the SiC solution varies, SiC polycrystals are likely to be formed by natural nucleation in the peripheral region. The SiC polycrystals thus formed are moved to the SiC seed crystal by the flow of the SiC solution. If a large amount of SiC polycrystals adhere to the SiC single crystal which has grown on the SiC seed crystal, the growth of the SiC single crystal may be impaired.
Production methods of an SiC single crystal intended for suppressing the formation of SiC polycrystals are disclosed in JP2004-323247A (Patent Literature 1) and JP2006-131433A (Patent Literature 2).
In the production method disclosed in Patent Literature 1, a heat insulating member made up of a black-lead cover or a graphite cover is disposed above a solution surface to suppress the heat release from the surface of the SiC solution. In the production method disclosed in Patent Literature 2, a heat insulating member is disposed in a free space above a crucible to adjust an in-plane temperature difference in the surface of an SiC solution to be within 40° C.